Organic nitrates and organic nitro compounds have been added to diesel fuels, as cetane improvers, for years. Since the 1930's, organic nitrates have been used in diesel fuels to increase cetane number and thereby achieve a level of auto-ignition sufficient to allow the operation of the diesel engine.
It has been discovered that the use of organic nitrogen-containing compounds selected from organic nitrates and/or organic nitro compounds, in gasoline, at specific treat rates, results in improved ignition properties and therefore benefits fuel economy, cold start ignition, lean burn, and reduced emissions. Improved ignition properties are evidenced by the reduction or complete elimination of engine misfires. The addition of organic nitrogen oxide containing compounds typically thought of as cetane improvers to gasoline appears counterintuitive. Because additives which increase the cetane number of diesel fuels are known to be pro-knock agents when added to gasoline, the discovery that the addition of an organic nitrate compound or an organic nitro compound to gasoline, at specific treat rates, will not negatively affect fuel octane and at the same time will improve the ignition properties of the fuel is surprising.
Cetane improver fuel additives, such as 2-ethylhexyl nitrate and di-tert-butyl peroxide, function at low temperatures (550-700K) of the internal combustion engine combustion cycle by promoting radical generation forcing ignition. The peak performance temperature regime of cetane improvers is centered around 625 degrees K. (about 352 C), above which all the —NO2 is used up and the additives are transformed to hydrocarbon fragments with similar combustion characteristics as the base fuel. Therefore development of combustion improvers that survive to higher temperatures in the combustion cycle of an internal combustion engine would contribute to more efficient combustion with predicable rates. Predictable fuel combustion efficiency can be manipulated to yield more power, torque, thermal efficiency, fuel economy, and lowered emissions. The major challenge in developing these additives is the fact that almost all organics begin thermal decomposition at about 673 degrees K. (400 C). This is close to the ignition point (about 800K, or 527 C) of fuel/air charge in internal combustion engines. Therefore, for an organic additive to function in the entire combustion regime of the engine, it has to survive at least up to 800 K.
What is needed is a gasoline combustion improver with a sufficiently high enough bond dissociation energy so that it will not dissociate at the low temperatures (550-700 degrees K.) of the internal combustion engine.